Here are some questions I received recently regarding VLAN
tagging on the VIO server. My answers are shown in green.

“Hi Chris,

Q: I’m trying to
understand when, where and why there would be the need to use ‘mkvdev –vlan
(etc.) on the VIOS, and I’m wondering whether you would be able to clarify this
for me, please.

Is it necessary to add
the VLAN tag devices to the SEA, or is it suffice to just have them defined
within the Virtual Ethernet itself which is part of the SEA?”

A:
It is suffice to simply define the VLAN ids assigned to the Virtual Ethernet
adapters associated with the SEA.

“Q: For completeness,
on the rare occasions I have done this, I have added the VLAN’s to the Virtual
Ethernet and also as VLAN devices on the VIOS (mkvdev –vlan etc.)”

A:
mkvdev –vlan is not necessary, unless
the VIOS needs to communicate with hosts on different VLANs i.e. you need an IP
address on the VIOS for each VLAN. This does not mean the SEA will bridge this
VLAN traffic for VIOCs.

“Q: The reason I
started thinking of this is, is because one of our customers wants to add new
VLAN’s to their SEA, but they’re not running Power7 hardware. Therefore, the
online method would be to add a new Virtual Adapter which contains the new VLAN
ID’s to the VIOS using DLPAR, then use chdev –dev (etc.) on the SEA to include
the new Virtual Ethernet.”

A:
Agreed. The “IBM PowerVM Virtualization Managing and Monitoring” Redbook
states: “If your system doesn’t support dynamic VLAN modifications and you are
modifying the VLAN list of a virtual Ethernet adapter that is configured in a
SEA with ha_mode enabled, the HMC will not allow you to reconfigure the list of
VLANs on that interface. You will need to add an additional virtual Ethernet
adapter and modify the virt_adapters list of the SEA, or modify the profile of
both Virtual I/O Servers and re-activate both Virtual I/O Servers at the same
time.”

“Q: From the phone
call I had, it would appear that the VLAN tags are included on the Virtual
Ethernet device, but have not been added to the SEA by running mkvdev –vlan
(etc. ) on the VIOS’s. This leads me to assume that the ‘mkvdev –vlan’ is
only required if there is a requirement to access the VIOS itself from a
particular VLAN. Am I right, or is there something I’m not understanding?
I’m unable to find documentation that explains the answer. Do you happen to
know?”

A:
That is also my understanding (based on my experience). On page 483 of the “IBM
PowerVM Virtualization Introduction and Configuration” Redbook , it states:
“The addition of VLAN interfaces to the SEA adapter is only necessary if the VIO
Server itself needs to communicate on these VLANs”.

“Q: Hi Chris,

We are trying to
associate a new entX Virtual Ethernet Trunk Device to an existing SEA. The new
device must be configured for VLAN tagging. The existing virtual Ethernet
adapter that (is already associated with the SEA) is not configured for VLAN
tagging. This device will remain associated to the SEA and continue to pass
untagged packets to the already configured network.

Ultimately the configuration
we want would be two entX devices associated with the existing SEA. One entX
device is configured for notagged packets and the other entX device is
configured for tagging.

Reply: “hmm ok I see
what you are saying, I will give it a go and tell you how it turns out...thanks.
ok finally got around to testing using a VIOS at DR site. Created
new virtual adapter PVID 55 and VID 888 (ent9) then added it to the existing
SEA as shown below: